The present invention relates to a fluorescent lamp operating apparatus and to a compact self-ballasted fluorescent lamp. The present invention relates more specifically to a dimmable fluorescent lamp operating apparatus and to a dimmable compact self-ballasted fluorescent lamp.
Fluorescent lamps have several advantages over incandescent lamps. For example, fluorescent lamps provide high efficiency operation and longer life. Because of these advantages, fluorescent lamps have been used extensively as luminaires for household use. In a typical technique of accomplishing the dimming of a fluorescent lamp, either the lamp current or lamp power is adjusted with a reference signal so as to control (dim) the brightness of the fluorescent lamp. More concretely, either the detection of a lamp current or lamp power is conducted and the switching frequency of the inverter circuit is feedback controlled so that the detected value becomes a predetermined lamp current or lamp power. An example of a lamp operating apparatus with such dimming capability is disclosed in JP Kokai Publication No. H09-204989.
According to such a published lamp operating apparatus, a signal proportional to the lamp power and a reference signal are subjected to comparison operation by an OP amplifier and based on a result of the comparison operation, the switching frequency of the inverter circuit is feedback controlled. As the switching frequency increases, the lamp power is reduced. As a result, the brightness of the fluorescent lamp decreases. On the other hand, as the switching frequency decreases, the lamp power increases. As a result, the brightness of the fluorescent lamp increases. At this time, the frequency characteristic bandwidth of the feedback controlling circuit for control of the lamp power is switched as follows. That is, when the lamp power is relatively small, the frequency characteristic bandwidth is made wider. On the other hand, when the lamp power is relatively great, the frequency characteristic bandwidth is made narrower. In other words, the frequency characteristic bandwidth of the feedback controlling circuit is varied depending upon the lamp power. The reason for this is to compensate unstable operation (oscillation) of the feedback controlling circuit, thereby to accomplish stable lamp dimming control from a high to a low lamp power state.
It is generally known in the art that discharge lamps, such as fluorescent lamps, gradually vary in their lamp characteristic (e.g., the electrical characteristic) during the transition to such a state that the temperature has become stable. Because of this, when a fluorescent lamp is turned on using a conventional circuit configuration of the type describe above, the following may occur. For example, in one case, it is possible to satisfactory accomplish lamp dimming control when the fluorescent lamp is sufficiently heated up to its high temperature state, while it is difficult to accomplish lamp dimming control when the fluorescent lamp is placed still in its low temperature state, and conversely, in another case, it is difficult to accomplish lamp dimming control when the fluorescent lamp is sufficiently heated up to its high temperature state, while on the other hand it is possible to satisfactory accomplish lamp dimming control when the fluorescent lamp is placed still in its low temperature state and consequently the feedback controlling circuit may become unstable in operation or generate oscillation because of the difference in lamp characteristic between the high temperature state and the low temperature state. Particularly, when the lamp power is small and the lamp temperature is low or when the lamp power is great and the lamp temperature is low, the feedback controlling circuit is likely to become unstable in operation or generate oscillation. Such lamp unstable operation (oscillation) may cause lamp flicker or produce some inconvenience (circuit failure in the worst case).
Bearing in mind the above problems with the prior art techniques, the present invention was made. Accordingly, a major object of the present invention is to provide a fluorescent lamp operating apparatus and a compact self-ballasted fluorescent lamp capable of accomplishing stable lamp dimming control, regardless of the temperature of the fluorescent lamp.
The present invention provides a dimmable fluorescent lamp operating apparatus which comprises a fluorescent lamp, electrical characteristic detecting means for detecting an electrical characteristic of the fluorescent lamp, an inverter circuit for driving the fluorescent lamp, and a feedback controlling circuit for controlling the drive frequency of the inverter circuit such that the electrical characteristic of the fluorescent lamp becomes a predetermined value, wherein the feedback controlling circuit includes temperature detecting means for detecting the temperature of the fluorescent lamp and wherein the frequency characteristic bandwidth of the feedback controlling circuit is varied based on the detected fluorescent lamp temperature.
In an embodiment of the present invention, the feedback controlling circuit has functions such that when the detected fluorescent lamp temperature is relatively high, the frequency characteristic bandwidth is made narrower, while when the detected fluorescent lamp temperature is relatively low, the frequency characteristic bandwidth is made wider.
It is preferred that the temperature detecting means be a thermally sensitive resistance element.
The present invention provides a compact self-ballasted fluorescent lamp comprising a fluorescent lamp, a ballast circuit, and a base wherein the fluorescent lamp is integrally formed with the ballast circuit and the base which are electrically connected to the fluorescent lamp. The ballast circuit comprises electrical characteristic detecting means for detecting an electrical characteristic of the fluorescent lamp, an inverter circuit for driving the fluorescent lamp, and a feedback controlling circuit for controlling the drive frequency of the inverter circuit such that the electrical characteristic of the fluorescent lamp becomes a predetermined value, wherein the feedback controlling circuit includes temperature detecting means for detecting the temperature of the fluorescent lamp and wherein the frequency characteristic bandwidth of the feedback controlling circuit is varied based on the detected fluorescent lamp temperature.
In an embodiment of the present invention, the feedback controlling circuit has functions such that when the detected fluorescent lamp temperature is relatively high, the frequency characteristic bandwidth is made narrower, while when the detected fluorescent lamp temperature is relatively low, the frequency characteristic bandwidth is made wider.
It is preferred that the temperature detecting means be a thermally sensitive resistance element.
Preferably, the thermally sensitive resistance element is so disposed as to be spaced at least 10 mm apart from a tube end at which an electrode of the fluorescent lamp is sealed.